Aircraft air speed control



y 4,19448 F. w. MEREDITH 2,352,878

AIRCRAFT AIR SPEED CONTROL Filed June 13, 1939 Patented July 4, 1944 I, amonmnmsrnsn ooNraor.

Frederick William MeredithQ London, England, assignor to S. Smith & Sons (Motor Accessories) Limited, London, England, a British company Application June 13, 1939, Serial No. 278,940 -In Great Britain June 14, 1938 i g 6 Claims. (01. 24 1-78) This invention relates the control of aircraft according to air speed. The-invention is con- I cerned with apparatus of the known kind for. adlusting a control surface oi. an aircraft, such as an elevatoncomprising a movable control member whichis subjected to a dynamicpressure produced by the air, means for applying an opposing biasing force to the control member and means operated by the control member automatically to adjust the control, surface of the aircraft such asto maintain a constant air speed. It is known to control the elevators of an aircraft automatically in' accordance with the indicated airspeed (i. e. Rt V where Vis the true air speed and R is the relative density.

where p is the actual density of the air and,

is the conventional airdensity at ground level) to maintain the speed constant by varying the trifugal air ump l5.

adjustment of the elevators according to the difference' between a dynamic pressure produced by the air, due to the motion of the aircrafhand a biasing force consisting ofa spring which may be adjustable. The ,term .dynamic pressure is herein used to indicate the pressure due to motion (1. e. lo: W where p is the air density, V the velocity of motion andk a constant depending on the type of exploration head employed).

According to the present invention there is provided an apparatus of the kind referred to for controlling aircraft wherein the opposing biasing force is applied tothe control mem- 1 her by means of fluid pressure. For producing the fluid pressure there is. conveniently provided a pump, of which the output pressure increases with an increase of fluid density; so that by em.

ploying air as the fluid the pressuremay be made proportional to the air density. The control will then be independent of the actual density of the aid and therefore in accordance with true air speed. Means is preferably providedfor varying the speed of the pum to vary the speed of a the aircraft This pump outlet pressure may be designated the "datum pressure and will be understood to accordingly; The indication of truej'airspeed is obtained when the dynamic pressure Qbalances the pump pressure. I In a preferred construction the control member comprises a flexible. diaphragm forming at one side the wall of a chamber connected toa Pitot tube and at the ,other side a wall of a chamber connected to'a source of opposing fluid pressure. i.

Onespeciflc embodiment of the inventionis illustrated diagrammatically and by way of examplein the accompanying drawing. I

Referring to the drawing, the control membe is constituted by a flexible diaphragm ill mounted in a housing consisting of rigid walls ii and 12 at opposite sides of the. diaphragm. .The

chamber formed by the diaphragm and the wall communicates with a Pitot head l3, and the. chamber formed by the diaphragm and the wall I! communicates by a-pipe with a cen- The diaphragm. ill isconnected toa spindle is extending through the wall l2 of the housing for operation of the elevator ofan aircraft through a pneumatic servomotor in known manner. The spindle i6 is connected to a piston valve ll movablein a cylinder 18 forcontrolling the supply of compressed air through a pipe I! to. opposite sides of a piston 20 of a servomotor 2i. The piston is connected by ,a linkage 22 to the elevator indicated at 23. To provide theneces'sary follow-up, the piston'isalso connected to one arm of a lever 25 pivoted on a fixed bracket 25, the

other arm of the lever being connected by a link 21 to the, cylinder i8, Known centering mechanism comprising a viscous element 2! and a spring "is provided for the purpose ofrecentering the yalve casing l8 and hence the diaphragrn ill whenthe trimming positionofthe elevator is varied.

The pum is driven for example by an .electric motor from a batteryill, the speedol the m'otor being adjustable by means'ofa rheostat include the prevailing static pressure as well as the dynamic pressure due to the action of the pump.

According to a iurther feature of the invention a tachometer is coupled to the pum for providingran indication of true air speed, and the tachometer scale is conveniently calibrated ii. The pump is also connected to a tachometer 32 which] is .calibrated' for air speed.

In operation, the air pressure providedby the pump i5 is appliedto the diaphragm III in o'pposition to the dynamic pressure at the Pitot head l3 due to the motion of the aircraft. When the pump it is run at constant speed, movements of the diaphragm will only result from changes of true air speed because its movement is independent of the actual density of the air and will therefore control the elevator 23 through the servomotor 2| according to true air speed, so as to maintain the speed of the aircraft substantially constant. The tachometer 82 provides, under steady conditions, an indication of true air speed. To vary the true air speed it is only necessary to vary the speed 02 .the pump l5 until the desired air speed is indicated on the tachometer 32. If the pressure produced by the pump I5 is not of the same order 'may be applied to the pump l5, for instance by including a constant current devicein the motor circuit, and the aircraft will then be controlled by the flexible diaphragm in accordance with the indicated air speed instead of true air speed," although the tachometer will still in dicate the true air speed.

It will be understood that the invention is not restricted to the specific embodiments hereinbefore described; for instance, means other than a pump may be employed for adjusting the fluid pressure'a-pplied to the control member.

I claim:

1. Apparatus for adjusting a control device for regulating the speed of an aircraft comprising a movable control member operatively connected with said control device, means operatively communicating with said control member to apply thereto a pressure in one direction which is the algebraic sum of the prevailing static pressure and a pressure proportional to the dynamic pressure of the air due to the motion of said aircraft therethrough, a constant speed motor, an air pump driven by said motor, the outlet pressure of said pump increasing with an increase in air density, and means connecting theoutlet of the pump with said control member for applying to the latter an opposed biassing pressure deter- 'will to run at selected constant speeds, an air pump driven by said motor, th outlet pressure of said pump increasing with an increase in air density, and means connecting the outlet of the pump with said control member for applying to the latter an opposed biassing pressure determined by the selected speed of said pump and air density.

3. In an aircraft having a control device for able control member operatively connected with I adjusting the speed thereof; apparatus for adjusting said control device comprising a movsaid control device, means operatively communicating with said control member to apply thereto a pressure in one direction whichv is the algebraic sum of the prevailing static pressure and a pressure proportional to the dynamic pressure of the air due to the motion of saidaircraft therethrough, a constant speed motor, an

air pump driven by said motor, the outlet pres-- sure of saidpum increasing with an increase in air density, and means connecting the outlet of the pump with said control member for applying to the latter an opposed biassing pressure determined by the speed of said pump and,

air density. 4. In an air speed responsive device for automatically controlling the operation of an air-- craft, the combination including an expansible container subject to air pressure variable, with the juxtaposed walls of said containers for operating, said. motor, and means adjustable at-will for altering the datum air pressure in said sec- I I -ond container. I a

5. In an air speed responsive device for auto matically controlling the air speed of an aircraft, the combination including an expansible container subject to air pressure variable with 1 air speed a secondexpansible container subject to a datum air pressure varying with altitude in the same manner as said air-speed-variable I H air pressure, a constant speed air pump communicatingwith said second containerto supply said datum air pressure, said containers being so juxtaposed that the expansion of each is opposed only by the expansion of the other, a

'servomotor for controlling the air speed of the' craft, and controlling means responsive to displacement of the juxtaposed walls of said containers for operating said servo-motor whereby said device is rendered of altitude.

a datum'air pressure varying with altitude in the same manner as said air-'speed-variable air pressure, a constant speed air pump communicatin with saidsecond container to supply said datum air pressure, said containers being so juxtaposed that the expansion of each is opposed onlyby the expansion of the other, a servomotor'for controlling the air speed of. the craft, controlling means responsive to displacement of the juxtaposed wallsof said containers for oper-; ating said servomotor and means for adjusting the-speed of said constant speed air pump at will.

FREDERICK MEREDITH.

independent of changes I 

